Non-polar a-plane gallium nitride thin films grown by metalorganic chemical vapor deposition

ABSTRACT

Non-polar (11{overscore (2)}0) a-plane gallium nitride (GaN) films with planar surfaces are grown on (1{overscore (1)}02) r-plane sapphire substrates by employing a low temperature nucleation layer as a buffer layer prior to a high temperature growth of the non-polar (11{overscore (2)}0) a-plane GaN thin films.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit under 35 U.S.C. §119(e) ofthe following copending and commonly-assigned U.S. Provisional PatentApplication Serial No. 60/372,909, entitled “NON-POLAR GALLIUM NITRIDEBASED THIN FILMS AND HETEROSTRUCTURE MATERIALS,” filed on Apr. 15, 2002,by Michael D. Craven, Stacia Keller, Steven P. DenBaars, Tal Margalith,James S. Speck, Shuji Nakamura, and Umesh K. Mishra, attorneys docketnumber 30794.95-U.S. Pat. No. 1, which application is incorporated byreference herein.

[0002] This application is related to the following co-pending andcommonly-assigned United States Utility Patent Applications:

[0003] Ser. No. ______, entitled “NON-POLAR (Al,B,IN,GA)N QUANTUM WELLAND HETEROSTRUCTURE MATERIALS AND DEVICES,” filed on same date herewith,by Michael D. Craven, Stacia Keller, Steven P. DenBaars, Tal Margalith,James S. Speck, Shuji Nakamura, and Umesh K. Mishra, attorneys docketnumber 30794.101-US-U1; and

[0004] Ser. No. ______, entitled “DISLOCATION REDUCTION IN NON-POLARGALLIUM NITRIDE THIN FILMS,” filed on same date herewith, by Michael D.Craven, Steven P. DenBaars and James S. Speck, attorneys docket number30794.102-US-U1;

[0005] both of which applications are incorporated by reference herein.

1. FIELD OF THE INVENTION

[0006] The invention is related to semiconductor materials, methods, anddevices, and more particularly, to non-polar a-plane gallium nitride(GaN) thin films grown by metalorganic chemical vapor deposition(MOCVD).

2. DESCRIPTION OF THE RELATED ART

[0007] (Note: This application references a number of different patents,applications and/or publications as indicated throughout thespecification by one or more reference numbers. A list of thesedifferent publications ordered according to these reference numbers canbe found below in the section entitled “References.” Each of thesepublications is incorporated by reference herein.)

[0008] Polarization in wurtzite III-nitride compounds has attractedincreased attention due to the large effect polarization-inducedelectric fields have on heterostructures commonly employed innitride-based optoelectronic and electronic devices. Nitride-basedoptoelectronic and electronic devices are subject topolarization-induced effects because they employ nitride films grown inthe polar c-direction [0001], the axis along which the spontaneous andpiezoelectric polarization of nitride films are aligned. Since the totalpolarization of a nitride film depends on the composition and strainstate, discontinuities exist at interfaces between adjacent devicelayers and are associated with fixed sheet charges that give rise tointernal electric fields.

[0009] Polarization-induced electric fields, although advantageous fortwo-dimensional electron gas (2DEG) formation in nitride-basedtransistor structures, spatially separate electrons and hole wavefunctions in quantum well (QW) structures, thereby reducing carrierrecombination efficiencies in QW based devices, such as laser diodes andlight emitting diodes. See References 1. A corresponding reduction inoscillator strength and red-shift of optical transitions have beenreported for AlGaN/GaN and GaN/InGaN quantum wells grown along the GaNc-axis. See References 2-7.

[0010] A potential means of eliminating the effects of thesepolarization-induced fields is through the growth of structures indirections perpendicular to the GaN c-axis (non-polar) direction. Forexample, m-plane AlGaN/GaN quantum wells have recently been grown onlithium aluminate substrates via plasma-assisted molecular beam epitaxy(MBE) without the presence of polarization-induced electric fields alongthe growth direction. See Reference 8.

[0011] Growth of a-plane nitride semiconductors also provides a means ofeliminating polarization-induced electric field effects in wurtzitenitride quantum structures. For example, in the prior art, a-plane GaNgrowth had been achieved on r-plane sapphire via MOCVD and molecularbeam epitaxy (MBE). See References 9-15. However, the film growthreported by these early efforts did not utilize a low temperature bufferlayer and did not possess smooth planar surfaces, and therefore, theselayers were poorly suited for heterostructure growth and analysis.Consequently, there is a need for improved methods of growing films thatexhibit improved surface and structural quality as compared topreviously reported growth of GaN on r-plane sapphire via MOCVD.

SUMMARY OF THE INVENTION

[0012] The present invention describes a method for growingdevice-quality non-polar aplane GaN thin films via MOCVD on r-planesapphire substrates. The present invention provides a pathway tonitride-based devices free from polarization-induced effects, since thegrowth direction of non-polar a-plane GaN thin films is perpendicular tothe polar c-axis. Polarization-induced electric fields will have minimaleffects, if any, on (Al,B,In,Ga)N device layers grown on non-polara-plane GaN thin films.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Referring now to the drawings in which like reference numbersrepresent corresponding parts throughout:

[0014]FIG. 1 is a flowchart that illustrates the steps of the MOCVDprocess for the growth of non-polar (11{overscore (2)}0) a-plane GaNthin films on (1{overscore (1)}20) r-plane sapphire, according to thepreferred embodiment of the present invention;

[0015]FIG. 2(a) shows a 2θ-ω diffraction scan that identifies the growthdirection of the GaN film as (1{overscore (1)}20) a-plane GaN;

[0016]FIG. 2(b) is a compilation of off-axis φ scans used to determinethe in-plane epitaxial relationship between GaN and r-sapphire, whereinthe angle of inclination ψ used to access the off-axis reflections isnoted for each scan;

[0017]FIG. 2(c) is a schematic illustration of the epitaxialrelationship between the GaN and r-plane sapphire;

[0018] FIGS. 3(a) and 3(b) are cross-sectional and plan-viewtransmission electron microscopy (TEM) images, respectively, of thedefect structure of the a-plane GaN films on r-plane sapphire; and

[0019] FIGS. 4(a) and 4(b) are atomic force microscopy (AFM) amplitudeand height images, respectively, of the surface of the as-grown a-planeGaN films.

DETAILED DESCRIPTION OF THE INVENTION

[0020] In the following description of the preferred embodiment,reference is made to the accompanying drawings which form a part hereof,and in which is shown by way of illustration a specific embodiment inwhich the invention may be practiced. It is to be understood that otherembodiments may be utilized and structural changes may be made withoutdeparting from the scope of the present invention.

[0021] Overview

[0022] The present invention describes a method for growing devicequality non-polar (11{overscore (2)}0) a-plane GaN thin films via MOCVDon (1{overscore (1)}02) r-plane sapphire substrates. The method employsa low-temperature buffer layer grown at atmospheric pressure to initiatethe GaN growth on r-plane sapphire. Thereafter, a high temperaturegrowth step is performed at low pressures, e.g., ˜0.1 atmospheres (atm)in order to produce a planar film.

[0023] Planar growth surfaces have been achieved using the presentinvention. Specifically, the in-plane orientation of the GaN withrespect to the r-plane sapphire substrate has been confirmed to be[0001]_(GaN)∥[{overscore (1)}101]_(sapphire) and ∥[{overscore(1)}100]_(GaN)∥[11{overscore (2)}0]_(sapphire).

[0024] The resulting films possess surfaces that are suitable forsubsequent growth of (Al,B,In,Ga)N device layers. Specifically,polarization-induced electric fields will have minimal effects, if any,on (Al,B,In,Ga)N device layers grown on non-polar a-plane GaN baselayers.

[0025] Process Steps

[0026]FIG. 1 is a flowchart that illustrates the steps of the MOCVDprocess for the growth of non-polar (11{overscore (2)}0) a-plane GaNthin films on a (1{overscore (1)}20) r-plane sapphire substrate,according to the preferred embodiment of the present invention. Thegrowth process was modeled after the two-step process that has becomethe standard for the growth of c-GaN on c-sapphire. See Reference 16.

[0027] Block 100 represents loading of a sapphire substrate into avertical, close-spaced, rotating disk, MOCVD reactor. For this step,epi-ready sapphire substrates with surfaces crystallographicallyoriented within +/−2° of the sapphire r-plane (1{overscore (1)}20) maybe obtained from commercial vendors. No ex-situ preparations need beperformed prior to loading the sapphire substrate into the MOCVDreactor, although ex-situ cleaning of the sapphire substrate could beused as a precautionary measure.

[0028] Block 102 represents annealing the sapphire substrate in-situ ata high temperature (>1000° C.), which improves the quality of thesubstrate surface on the atomic scale. After annealing, the substratetemperature is reduced for the subsequent low temperature nucleationlayer deposition.

[0029] Block 104 represents depositing a thin, low temperature, lowpressure, nitride-based nucleation layer as a buffer layer on thesapphire substrate. In the preferred embodiment, the nucleation layer iscomprised of, but is not limited to, 1-100 nanometers (nm) of GaN and isdeposited at low temperature, low pressure depositing conditions ofapproximately 400-900° C. and 1 atm. Such layers are commonly used inthe heteroepitaxial growth of c-plane (0001) nitride semiconductors.Specifically, this depositing step initiates GaN growth on the r-planesapphire substrate.

[0030] After depositing the nucleation layer, the reactor temperature israised to a high temperature, and Block 106 represents growing thenon-polar (11{overscore (2)}0) a-plane GaN thin films on the substrate.In the preferred embodiment, the high temperature growth conditionscomprise, but are not limited to, approximately 1100° C. growthtemperature, approximately 0.2 atm or less growth pressure, 30 μmol perminute Ga flow, and 40,000 μmol per minute N flow, thereby providing aV/III ratio of approximately 1300). In the preferred embodiment, theprecursors used as the group III and group V sources aretrimethylgallium and ammonia, respectively, although alternativeprecursors could be used as well. In addition, growth conditions may bevaried to produce different growth rates, e.g., between 5 and 9 Å persecond, without departing from the scope of the present invention.Non-polar GaN approximately 1.5 μm thick have been grown andcharacterized.

[0031] Upon completion of the high temperature growth step, Block 108represents cooling the non-polar (11{overscore (2)}0) a-plane GaN thinfilms under a nitrogen overpressure.

[0032] Finally, Block 110 represents the end result of the processingsteps, which is a nonpolar (11{overscore (2)}0) a-plane GaN film on anr-plane sapphire substrate. Potential device layers to be manufacturedusing these process steps to form a non-polar (11{overscore (2)}0)a-plane GaN base layer for subsequent device growth include laser diodes(LDs), light emitting diodes (LEDs), resonant cavity LEDs (RC-LEDs),vertical cavity surface emitting lasers (VCSELs), high electron mobilitytransistors (HEMTs), heterojunction bipolar transistors (HBTs),heterojunction field effect transistors (HFETs), and UV and near-UVphotodetectors.

[0033] Experimental Results

[0034] The crystallographic orientation and structural quality of theas-grown GaN films and r-plane sapphire were determined using a Philips™four-circle, high-resolution, x-ray diffractometer (HR-XRD) operating inreceiving slit mode with four bounce Ge(220)-monochromated Cu Kαradiation and a 1.2 mm slit on the detector arm. Convergent beamelectron diffraction (CBED) was used to determine the polarity of thea-GaN films with respect to the sapphire substrate. Plan-view andcross-section transmission electron microscopy (TEM) samples, preparedby wedge polishing and ion milling, were analyzed to define the defectstructure of a-GaN. A Digital Instruments D3000 Atomic Force Microscope(AFM) in tapping mode produced images of the surface morphology.

[0035]FIG. 2(a) shows a 2θ-ω diffraction scan that identifies the growthdirection of the GaN film as (11{overscore (2)}0) a-plane GaN. The scandetected sapphire (1{overscore (1)}02), (2{overscore (2)}04), and GaN(11{overscore (2)}0) reflections. Within the sensitivity of thesemeasurements, no GaN (0002) reflections corresponding to 2θ=34.604° weredetected, indicating that there is no c-plane (0002) content present inthese films, and thus instabilities in the GaN growth orientation arenot a concern.

[0036]FIG. 2(b) is a compilation of off-axis φ scans used to determinethe in-plane epitaxial relationship between GaN and r-sapphire, whereinthe angle of inclination ψ used to access the off-axis reflections isnoted for each scan. Having confirmed the a-plane growth surface,off-axis diffraction peaks were used to determine the in-epitaxialrelationship between the GaN and the r-sapphire. Two sample rotations φand ψ were adjusted in order to bring off-axis reflections into thescattering plane of the diffractometer, wherein φ is the angle ofrotation about the sample surface normal and ψ is the angle of sampletilt about the axis formed by the intersection of the Bragg andscattering planes. After tilting the sample to the correct ψ for aparticular off-axis reflection, φ scans detected GaN (10{overscore(1)}0), (10{overscore (1)}1), and sapphire (0006) peaks, as shown inFIG. 2(b). The correlation between the φ positions of these peaksdetermined the following epitaxial relationship:[0001]_(GaN)∥[{overscore (1)}101]_(sapphire) and [{overscore(1)}100]_(GaN)∥[11{overscore (2)}0]_(sapphire).

[0037]FIG. 2(c) is a schematic illustration of the epitaxialrelationship between the GaN and r-plane sapphire. To complement thex-ray analysis of the crystallographic orientation, the a-GaN polaritywas determined using CBED. The polarity's sign is defined by thedirection of the polar Ga—N bonds aligned along the GaN c-axis; thepositive c-axis [0001] points from a gallium atom to a nitrogen atom.Consequently, a gallium-face c-GaN film has a [0001] growth direction,while a nitrogen-face c-GaN crystal has a [000{overscore (1)}] growthdirection. For a-GaN grown on r-sapphire, [0001]_(GaN) is aligned withthe sapphire c-axis projection [{overscore (1)}101]_(sapphire), andtherefore, the epitaxial relationships defined above are accurate interms of polarity. Consequently, the positive GaN c-axis points in samedirection as the sapphire c-axis projection on the growth surface (asdetermined via CBED). This relationship concurs with the epitaxialrelationships previously reported by groups using a variety of growthtechniques. See References 9, 12 and 14. Therefore, the epitaxialrelationship is specifically defined for the growth of GaN on an r-planesapphire substrate.

[0038] FIGS. 3(a) and 3(b) are cross-sectional and plan-view TEM images,respectively, of the defect structure of the a-plane GaN films on anr-plane sapphire substrate. These images reveal the presence of line andplanar defects, respectively. The diffraction conditions for FIGS. 3(a)and 3(b) are g=0002 and g=10{overscore (1)}0, respectively.

[0039] The cross-sectional TEM image in FIG. 3(a) reveals a largedensity of threading dislocations (TD's) originating at the sapphire/GaNinterface with line directions parallel to the growth direction[11{overscore (2)}0]. The TD density, determined by plan view TEM, was2.6×10¹⁰ cm⁻². With the TD line direction parallel to the growthdirection, pure screw dislocations will have Burgers vectors alignedalong the growth direction b=±[11{overscore (2)}0]) while pure edgedislocations will have b=±[0001]. The reduced symmetry of the a-GaNsurface with respect to c-GaN complicates the characterization of mixeddislocations since the crystallographically equivalent [11{overscore(2)}0] directions cannot be treated as the family<11{overscore (2)}0>.Specifically, the possible Burgers vectors of mixed dislocations can bedivided into three subdivisions: (1) b=±[1{overscore (2)}10] b and (3)b=±[{overscore (2)}110], (2) b=±[11{overscore (2)}0]±[0001], and (3)b=[11{overscore (2)}0]±[1{overscore (2)}10] and b=±[11{overscore(2)}0]±[{overscore (2)}110].

[0040] In addition to line defects, the plan view TEM image in FIG. 3(b)reveals the planar defects observed in the a-GaN films. Stacking faultsaligned perpendicular to the c-axis with a density of 3.8×10 ⁵ cm⁻¹ wereobserved in the plan-view TEM images. The stacking faults, commonlyassociated with epitaxial growth of close-packed planes, most likelyoriginate on the c-plane sidewalls of three-dimensional (3D) islandsthat form during the initial stages of the high temperature growth.Consequently, the stacking faults are currently assumed to be intrinsicand terminated by Shockley partial dislocations of opposite sign.Stacking faults with similar characteristics were observed in a-planeAlN films grown on r-plane sapphire substrates. See Reference 17. Thestacking faults have a common faulting plane parallel to theclose-packed (0001) and a density of ˜3.8×10⁵ cm⁻¹ .

[0041] Omega rocking curves were measured for both the GaN on-axis(11{overscore (2)}0) and off-axis (10{overscore (1)}1) reflections tocharacterize the a-plane GaN crystal quality. The full-widthhalf-maximum (FWHM) of the on-axis peak was 0.29° (1037″), while theoff-axis peak exhibited a larger orientational spread with a FWHM of0.46° (1659″). The large FWHM values are expected since themicrostructure contains a substantial dislocation density. According tothe analysis presented by Heying et al. for c-GaN films on c-sapphire,on-axis peak widths are broadened by screw and mixed dislocations, whileoff-axis widths are broadened by edge-component TD's (assuming the TDline is parallel to the film normal). See Reference 18. A relativelylarge edge dislocation density is expected for a-GaN on r-sapphire dueto the broadening of the off-axis peak compared to the on-axis peak.Additional microstructural analyses are required to correlate a-GaN TDgeometry to rocking curve measurements.

[0042] FIGS. 4(a) and 4(b) are AFM amplitude and height images,respectively, of the surface of the as-grown a-plane GaN film. Thesurface pits in the AFM amplitude image of FIG. 4(a) are uniformlyaligned parallel to the GaN c-axis, while the terraces visible in theAFM height image of FIG. 4(b) are aligned perpendicular to the c-axis.

[0043] Although optically specular with a surface RMS roughness of 2.6nm, the a-GaN growth surface is pitted on a sub-micron scale, as can beclearly observed in the AFM amplitude image shown in FIG. 4(a). It hasbeen proposed that the surface pits are decorating dislocationterminations with the surface; the dislocation density determined byplan view TEM correlates with the surface pit density within an order ofmagnitude.

[0044] In addition to small surface pits aligned along GaN c-axis[0001], the AFM height image in FIG. 4(b) reveals faint terracesperpendicular to the c-axis. Although the seams are not clearly definedatomic steps, these crystallographic features could be the early signsof the surface growth mode. At this early point in the development ofthe a-plane growth process, neither the pits nor the terraces have beencorrelated to particular defect structures.

REFERENCES

[0045] The following references are incorporated by reference herein:

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[0047] 2. O. Ambacher, J. Smart, J. R. Shealy, N. G. Weimann, K. Chu, M.Murphy, W. J. Schaff, L. F. Eastman, R. Dimitrov, L. Wittmer, M.Stutzmann, W. Rieger, and J. Hilsenbeck, J. Appl. Phys. 85, 3222 (1999).

[0048] 3. I. Jin Seo, H. Kollmer, J. Off, A. Sohmer, F. Scholz, and A.Hangleiter, Phys. Rev. B 57, R9435 (1998).

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[0050] 5. P. Lefebvre, J. Allegre, B. Gil, H. Mathieu, N. Grandjean, M.Leroux, J. Massies, and P. Bigenwald, Phys. Rev. B 59, 15363 (1999).

[0051] 6. P. Lefebvre, A. Morel, M. Gallart, T. Taliercio, J. Allegre,B. Gil, H. Mathieu, B. Damilano, N. Grandjean, and J. Massies, Appl.Phys. Lett. 78, 1252 (2001).

[0052] 7. T. Takeuchi, C. Wetzel, S. Yamaguchi, H. Sakai, H. Amano, I.Akasaki, Y. Kaneko, S. Nakagawa, Y. Yamaoka, and N. Yamada, Appl. Phys.Lett. 73, 1691 (1998).

[0053] 8. P. Waltereit, O. Brandt, A. Trampert, H. T. Grahn, J.Menniger, M. Ramsteiner, M. Reiche, and K. H. Ploog, Nature (London 406,865 (2000).

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[0055] 10. C. J. Sun and M. Razeghi, Appl. Phys. Lett. 63, 973 (1993).

[0056] 11. T. Metzger, H. Angerer, O. Ambacher, M. Stutzmann, and E.Born, Phys. Status Solidi B 193, 391 (1996).

[0057] 12. T. Lei, K. F. Ludwig, Jr., and T. D. Moustakas, J. Appl.Phys. 74, 4430 (1993).

[0058] 13. C. R. Eddy, Jr., T. D. Moustakas, and J. Scanlon, J. Appl.Phys. 73, 448 (1993).

[0059] 14. T. D. Moustakas, T. Lei, and R. J. Molnar, Physica B 185, 36(1993).

[0060] 15. K. Iwata, H. Asahi, K. Asami, R. Kuroiwa, and S. Gonda, Jpn.J. Appl. Phys., Part 236, L661 (1997).

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[0064] Conclusion

[0065] This concludes the description of the preferred embodiment of thepresent invention. The following describes some alternative embodimentsfor accomplishing the present invention.

[0066] For example, as the inclusions in the description above indicate,there are many modifications and variations of the MOCVD technique andequipment that could be used to grow non-polar (11{overscore (2)}0)a-plane GaN thin films on (1{overscore (1)}02) r-plane sapphiresubstrates. Moreover, different growth conditions may be optimal fordifferent MOCVD reactor designs. Many variations of this process arepossible with the variety of reactor designs currently being using inindustry and academia. Despite these differences, the growth parameterscan most likely be optimized to improve the quality of the films. Themost important variables for the MOCVD growth include growthtemperature, V/III ratio, precursor flows, and growth pressure.

[0067] In addition to the numerous modifications possible with the MOCVDgrowth technique, other modifications are possible. For example, thespecific crystallographic orientation of the r-plane sapphire substratemight be changed in order to optimize the subsequent epitaxial GaNgrowth. Further, r-plane sapphire substrates with a particular degree ofmiscut in a particular crystallographic direction might be optimal forgrowth.

[0068] In addition, the nucleation layer deposition is crucial toachieving epitaxial GaN films with smooth growth surfaces and minimalcrystalline defects. Other than optimizing the fundamental MOCVDparameters, use of AlN or AlGaN nucleation layers in place of GaN couldprove useful in obtaining high quality a-plane GaN films.

[0069] Further, although non-polar a-plan GaN thin films are describedherein, the same techniques are applicable to non-polar m-plane GaN thinfilms. Moreover, non-polar InN, AlN, and AlInGaN thin films could becreated instead of GaN thin films.

[0070] Finally, substrates other than sapphire substrate could beemployed for non-polar GaN growth. These substrates include siliconcarbide, gallium nitride, silicon, zinc oxide, boron nitride, lithiumaluminate, lithium niobate, germanium, aluminum nitride, and lithiumgallate.

[0071] In summary, the present invention describes the growth ofnon-polar (11{overscore (2)}0) a-plane GaN thin films on r-plane(1{overscore (1)}02) sapphire substrates by employing a low temperaturenucleation layer as a buffer layer prior to a high temperature growth ofthe epitaxial (11{overscore (2)}0) a-plane GaN films. The epitaxialrelationship is [0001]_(GaN)∥[{overscore (1)}101]_(sapphire) and[{overscore (1)}100] _(GaN)∥[11{overscore (2)}0]_(sapphire) with thepositive GaN c-axis pointing in the same direction as the sapphirec-axis projection on the growth surface.

[0072] The foregoing description of one or more embodiments of theinvention has been presented for the purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise form disclosed. Many modifications andvariations are possible in light of the above teaching. It is intendedthat the scope of the invention be limited not by this detaileddescription, but rather by the claims appended hereto.

What is claimed is:
 1. A method of growing a non-polar a-plane galliumnitride thin film on an r-plane substrate through metalorganic chemicalvapor deposition, comprising: (a) annealing the substrate; (b)depositing a nitride-based nucleation layer on the substrate; (c)growing the non-polar a-plane gallium nitride film on the nucleationlayer; and (d) cooling the non-polar a-plane gallium nitride film undera nitrogen overpressure.
 2. The method of claim 1, wherein the substrateis an r-plane sapphire substrate.
 3. The method of claim 2, wherein anin-plane orientation of the gallium nitride film with respect to ther-plane substrate is [0001_(]GaN)∥[{overscore (1)}101]_(sapphire) and[{overscore (1)}100]_(GaN)∥[11{overscore (2)}0]_(sapphire).
 4. Themethod of claim 1, wherein the substrate is selected from a groupcomprising silicon carbide, gallium nitride, silicon, zinc oxide, boronnitride, lithium aluminate, lithium niobate, germanium, aluminumnitride, and lithium gallate.
 5. The method of claim 1, wherein theannealing step (a) comprises a high temperature annealing of thesubstrate.
 6. The method of claim 1, wherein the depositing step (b)comprises a low temperature deposit of the nitride-based nucleationlayer on the substrate.
 7. The method of claim 1, wherein the depositingstep (b) comprises a low pressure deposit of the nitride-basednucleation layer on the substrate.
 8. The method of claim 1, wherein thelow temperature depositing conditions comprise approximately 400-900° C.and atmospheric pressure.
 9. The method of claim 1, wherein thedepositing step (b) initiates gallium nitride growth on the r-planesubstrate.
 10. The method of claim 1, wherein the nucleation layercomprises 1-100 nanometers of gallium nitride.
 11. The method of claim1, wherein the growing step (b) comprises a high temperature growth ofthe non-polar a-plane gallium nitride film on the nucleation layer. 12.The method of claim 11, wherein the high temperature layer is depositedat 0.2 atmospheres or less.
 13. The method of claim 11, wherein the hightemperature growth conditions comprise approximately 1100° C. growthtemperature, approximately 0.2 atmosphere or less growth pressure, 30μmol per minute gallium flow, and 40,000 μmol per minute nitrogen flow.14. The method of claim 1, wherein the growing step (b) produces theplanar gallium nitride film.
 15. A device manufactured using the methodof claim
 1. 16. A non-polar a-plane gallium nitride thin film on anr-plane substrate, wherein the thin film is created using a processcomprising: (a) annealing the substrate; (b) depositing a nitride-basednucleation layer on the substrate; (c) growing the non-polar a-planegallium nitride film on the nucleation layer; and (d) cooling thenon-polar a-plane gallium nitride film under a nitrogen overpressure.17. The thin film of claim 16, wherein the substrate is an r-planesapphire substrate.
 18. The thin film of claim 17, wherein an in-planeorientation of the gallium nitride films with respect to the r-planesubstrate is [0001]_(GaN)∥[{overscore (1)}101]_(sapphire) and[{overscore (1)}100]_(GaN)∥[11{overscore (2)}0]_(sapphire).
 19. The thinfilm of claim 16, wherein the substrate is selected from a groupcomprising silicon carbide, gallium nitride, silicon, zinc oxide, boronnitride, lithium aluminate, lithium niobate, germanium, aluminumnitride, and lithium gallate.
 20. The thin film of claim 16, wherein theannealing step (a) comprises a high temperature annealing of thesubstrate.
 21. The thin film of claim 16, wherein the depositing step(b) comprises a low temperature deposit of the nitride-based nucleationlayer on the substrate.
 22. The thin film of claim 16, wherein thedepositing step (b) comprises a low pressure deposit of thenitride-based nucleation layer on the substrate.
 23. The thin film ofclaim 16, wherein the low temperature depositing conditions compriseapproximately 400-900° C. and atmospheric pressure.
 24. The thin film ofclaim 16, wherein the depositing step (b) initiates gallium nitridegrowth on the r-plane substrate.
 25. The thin film of claim 16, whereinthe nucleation layer comprises 1-100 nanometers of gallium nitride. 26.The thin film of claim 16, wherein the growing step (b) comprises a hightemperature growth of the non-polar a-plane gallium nitride films on thenucleation layer.
 27. The thin film of claim 26, wherein the hightemperature layer is deposited at 0.2 atmospheres or less.
 28. The thinfilm of claim 26, wherein the high temperature growth conditionscomprise approximately 1100° C. growth temperature, approximately 0.2atmosphere or less growth pressure, 30 μmol per minute gallium flow, and40,000 μmol per minute nitrogen flow.
 29. The thin film of claim 16,wherein the growing step (b) produces a planar gallium nitride film. 30.A structure having a non-polar a-plane gallium nitride thin film on anr-plane substrate, comprising: (a) an annealed substrate; (b) anitride-based nucleation layer deposited on the substrate; and (c) anon-polar a-plane gallium nitride film grown on the nucleation layer andcooled under a nitrogen overpressure.
 31. The structure of claim 30,wherein the substrate is an r-plane sapphire substrate.
 32. Thestructure of claim 31, wherein an in-plane orientation of the galliumnitride film with respect to the r-plane substrate is[0001]_(GaN)∥[{overscore (1)}101]_(sapphire) and [{overscore(1)}100]_(GaN)∥[11{overscore (2)}0]_(sapphire).
 33. The structure ofclaim 30, wherein the substrate is selected from a group comprisingsilicon carbide, gallium nitride, silicon, zinc oxide, boron nitride,lithium aluminate, lithium niobate, germanium, aluminum nitride, andlithium gallate.